This invention relates to treating a waste stream, namely the solids tailings derived from the froth treating step of the hot water extraction process for recovering bitumen from bituminous sands, to modify the stream to a form in which it is amenable to conventional wet gravity concentration for the recovery of the contained titanium and zirconium values.
In the known hot water process for recovering bitumen, bituminous sands are agitated with water and steam in a tumbler and the resultant slurry is passed into a primary flotation vessel. The largest part of the coarse sand settles out in this vessel while the major portion of the bitumen floats to form froth, which is collected by a launder. A middlings stream is withdrawn from the vessel at its midpoint and is passed into an aerated secondary flotation vessel. Here a second froth product is produced which, after settling to reduce its water and solids content, is combined with the primary froth. This combined froth stream commonly comprises 63% bitumen, 8% solids and 29% water. The combined froth is deaerated and then sent to a circuit to separate the solids and water from the bitumen. This may be done by diluting the stream with naphtha and subjecting the diluted stream to two stage centrifugation. In the first stage, the froth is treated in a scroll-type centrifugal separator to remove the coarse and/or denser solids. In the second stage, the scroll product is passed through a disc-type centrifugal separator to remove the fine solids and water from the bitumen.
It is a peculiarity of the extraction process that it concentrates the bituminous sands' heavy minerals in the froth from the primary and secondary flotation vessels. These heavy minerals largely remain with the coarse solids produced as tailings. The invention has been developed in conjunction with scroll tailings from a dilution centrifuging circuit, and will be discussed hereinbelow in connection with this particular stream. However, it will be appreciated that the bitumen froth can be treated to separate bitumen and solids using a system other than dilution centrifuging, for example by cycloning the dehydrated froth to produce a comparable oily mass of solids. Therefore the term "solids tailings" used in the claims below is intended to describe a solids stream derived from a process for removing solids from froth produced during hot water extraction of bituminous sands and containing most or all of the heavy mineral portion of the froth solids. The term "solids tailings" is not to be limited to scroll separator tailings.
The solids tailings, preferably scroll separator tailings, provide the preferred feed stock of the present invention. These tailings are a black oily mass of mineral particles permeated and held together by bitumen, naphtha and water. The hydrocarbon content of the tailings usually ranges from 4% to 8% by weight and the water content from 5% to 10% by weight. Analyses have further shown that approximately 65% to 70% of the scroll tailings consists of minerals of low density, having specific gravities of 3.0 or less. Major constituents of these light materials are silica sand (SiO.sub.2), ferric oxide (Fe.sub.2 O.sub.3), and ferrous carbonate (FeCO.sub.3). The other minerals present have specific gravities ranging from about 3.0 to 4.6. Those at the lower end of this range (3.0 to 4.6) are iron aluminum silicates and other minerals of medium density. The remaining heavy minerals (ranging in specific gravity from about 4.0 to 4.6) contain the zirconium-based and titanium-based minerals that it is the purpose of the present invention to beneficiate. These heavy minerals include: Ilmenite (TiO.sub.2.FeO), Leucoxene, a general term commonly used to describe the alteration product of minerals containing TiO.sub.2 and FeO in various proportions, Rutile (TiO.sub.2), and Zircon (Zr SiO.sub.4).